Preheat oven to 200°C (400°F).
Put pastry base in your oven dish and prick with fork.
Slice tomatoes. Slice finely cheese.
Spread a generous layer of mustard. The spicy aftertaste of the Dijon mustard will disapear during baking.
Add a layer of cheese on top of the mustard and finish by a layer of tomatoes.
Dust thyme and pepper.
Bake for 30 minutes.